Add pagination with Kaminari to pictures#index

My website has over 250 images to load at once in the image browser. Each image is on the cloud so pulling the info for each of time was simply timing out. Request failed. Client couldn't had images to its text.

Basically, it adds Kaminari gem, paginates pictures and adds navigation at the bottom of the images browser. Upload link is repeated on each page.

Let me know how you want to improve it.